1. Field of the Invention
This invention relates to a sound motion picture camera which permits the sound filming by the use of a sound film cartridge and which further permits the silent filming by the use of a silent film cartridge.
2. Description of the Prior Art
The sound motion picture camera which permits selective use of a sound film cartridge and a silent film cartridge is entering its age of prosperity and usually, the sound motion picture camera of this type is provided with two motors for transporting the film.
One of the two motors is a film transport pawl driving motor which is used for the drive of the film transport pawl (first film transport means) for intermittently transporting the film at the exposure station of the camera, namely, at the region of the exposure aperture for filming. The other motor is a capstan driving motor which is used for the drive of a capstan (second film transport means) for continuously transporting the film at a constant speed at the sound recording station of the camera, namely, at the region of a recording magnetic head for the sound recording.
In the sound motion picture camera of this type, where sound filming is to be effected by the use of a sound film cartridge, a film loop is formed between the exposure station and the sound recording station so that the recording condition at the sound recording station may not be hindered by the pulsation of the film resulting from the intermittent transport of the film at the exposure station. Of course, in this case, the film loop must be always maintained at a predetermined length (usually, a loop length corresponding to the film length corresponding to 18 frames) in order to provide good synchronization between the image and the sound, but the film transport by the capstan at the sound recording station is apt to suffer from transport irregularity of the film due to slip between the capstan and the film and this may result in a variation in film loop length between the exposure station and the sound recording station. Accordingly, the general practice is to effect constant speed control of one of the two motors and effect variable speed control of the other motor to maintain a constant length of film loop. More particularly, for example, the constant speed control is effected on the capstan driving motor to provide a constant speed while a variable speed control is effected on the film transport pawl driving motor such that when the film loop is increased over a predetermined length, the speed of this motor is decreased to decrease the loop length by a signal from a loop detecting means for detecting any variation in the length of the film loop formed between the exposure station and the sound recording station and that when the film loop length is decreased below said predetermined length, the speed of the film transport pawl driving motor is increased to increase the film loop length.
In the sound motion picture camera of this type, the silent filming using a silent film cartridge is also possible and in silent filming, the capstan driving motor need not be operated, of course, and with regard to the film transport pawl driving motor, the variable speed control by the signal from loop detecting means as described above is not necessary but a constant speed control need only be effected so that a filming frame speed simply set may be obtained.
Thus, in the sound motion picture camera of this type, particularly as regards the film transport pawl driving motor, the mode of the speed control must be changed over to an entirely different mode from the sound filming using the sound film cartridge to the silent filming using the silent film cartridge and heretofore, as a method of automatically achieving this change-over, it has been usually practised, as proposed in U.S. Pat. No. 4,003,643 (issued on Jan. 18, 1977, granted to Treudenschuss et al. for the invention entitled "MOTION-PICTURE CAMERA ACCOMMODATING SILENT-FILM AND SOUND-FILM CASSETTES"), to install a mechanical cartridge type detecting means particularly at a position in the camera's cartridge loading chamber which enables discrimination of the difference in shape between the sound film cartridge and the silent film cartridge and to change over the speed control system for the film transport pawl driving motor from the constant speed control system to the variable speed control system by the film loop detecting means, in accordance with a mechanical signal from said detector means.
However, the provision of such means for mechanically detecting the difference in shape between the film cartridges has led to increased malfunctioning and could not avoid such fears as incomplete detection attributable to inappropriate loading of the film cartridge, or unsatisfactory mechanical contacts responsive to this detecting means, or malfunctioning attributable to non-contact.
On the other hand, as regards the change-over of the speed control of the film transport pawl driving motor, a method as proposed in U.S. patent Defensive Publication No. T920,009. (Published on Mar. 5, 1974, invented by Kosarko, title of the invention "CONTROL MEANS FOR A SOUND MOTION PICTURE CAMERA") has also been employed which comprises suitably effecting the constant speed control and the variable speed control of the film transport pawl driving motor in accordance with whether or not the loop detecting means has detected a variation in length of film loop, by simply utilizing only such film loop detecting means without resorting to the cartridge type detecting means as described above. More specifically, the method as proposed in this Defensive Publication No. T920,009 comprises controlling the film transport pawl driving motor to, for example, a rotational speed corresponding to the film transport speed of 20 frames/sec. of the film transport pawl when the film loop detecting means does not detect an increase in length of film loop over a predetermined length and controlling the film transport pawl driving motor to, for example, a rotational speed corresponding to the film transport speed of 16 frames/sec. of the film transport pawl to decrease the film loop length when the film loop detecting means detects an increase in length of film loop over the predetermined length. Therefore, in the sound motion picture camera employing such method, the film transport pawl driving motor is constantly controlled to a rotational speed corresponding to the filming speed of 20 frames/sec. during the silent filming using a silent film cartridge (because the film loop detecting means is not actuated at all), while during the sound filming using a sound film cartridge, the film transport pawl driving motor is variably controlled between two different rotational speeds corresponding to the filming speeds of 20 frames/sec. and 16 frames/sec. in accordance with the detection signal from the film loop detecting means (that is, controlled such that an average filming speed of 18 frames/sec. is obtained). This latter method entirely eliminates the cartridge type detecting means used in the method proposed in the aforementioned U.S. Pat. No. 4,003,643 and is advantageous in that it can avoid the above-noted inconveniences which result from the provision of the cartridge type detecting means. On the other hand, however, the latter method suffers from inconveniences as described below. In this method, where silent filming using a silent film cartridge is effected, the filming speed becomes 20 frames/sec. In conventional (sound or silent) motion picture projectors, the projection speed of 18 frames/sec. is standard and, if the silent film photographed by a sound motion picture camera employing the method as proposed in the Defensive Publication No. T920,009 is projected by the use of a conventional motion picture projector, the motion pictures reproduced will be ludicrous because of the difference between the filming speed and the projection speed.